This invention relates to an improved method for inhibiting the corrosion-causing tendency and coloration of olefin polymers or copolymers produced by using a Ziegler-type catalyst containing a halogen-containing compound as a catalyst ingredient and/or a carrier component, or olefin polymers or copolymers containing halogen components attributed to a polymerization catalyst and/or to post-halogenation, such as post-chlorinated olefin polymers or copolymers.
It is known that these halogen-containing olefin resins, because of their halogen component, cause corrosion or rust on metallic component parts such as molding machines or molds during the molding of the resins, or these resins or molded products prepared therefrom undergo coloration or deterioration.
The present invention pertains to an improved method for inhibiting the corrosion-causing tendency and coloration (or deterioration) of halogen-containing olefin polymers or copolymers (meant to include resin blends as well), which method avoids the aforesaid problems in a commercially advantageous manner by simple and inexpensive means with a good reproduciblity using a small amount of a non-toxic inhibitor, and which is not likely to cause other new problems.
More specifically, the present invention provides, in a method for inhibiting the corrosion-causing tendency and coloration of an olefin polymer or copolymer containing a halogen component by incorporating about 0.01 to about 5 parts by weight of a hydrotalcite, the improvement which comprises mixing an olefin polymer or copolymer, containing a halogen component attributed to a polymerization catalyst and/or post-halogenation, with a hydrotalcite of the formula EQU Mg.sub.1-x Al.sub.x (OH).sub.2 A.sup.n-.sub.x/n.mH.sub.2 O
wherein 0&lt;x.ltoreq.0.5, m is a positive number and A.sup.n- represents an anion having a valence of n, PA1 (i) a BET specific surface area of not more than 30 m.sup.2 /g, preferably not more than 20 m.sup.2 /g, and PA1 (ii) an average secondary particle size of not more than 5 microns, preferably not more than 1.5 microns, and preferably (iii) a crystallite size, in the &lt;003&gt; direction determined by an X-ray diffraction method, of at least 600 A, preferably at least 1000 A. PA1 wherein M is Mg, Ca or Zn, A is CO.sub.3 or HPO.sub.4, and x, y, z and a are positive numbers, PA1 (i) a BET specific surface area of not more than 30 m.sup.2 /g, preferably not more than 20 m.sup.2 /g, especially not more than 15 m.sup.2 /g, and PA1 (ii) an average secondary particle size of not more than 5 microns, preferably not more than 3 microns, especially not more than 1.5 microns, and preferably PA1 (iii) a crystallite size, in the &lt;003&gt; direction determined by an X-ray diffraction method of at least 600 A, preferably at least 1000 A.
or a product resulting from the surface-coating of said hydrotalcite with an anionic surface-active agent, said hydrotalcite having
In recent years, a number of new techniques have been developed for increasing the activity of halogen-containing Ziegler-type catalysts for the polymerization or copolymerization of olefins. This has consequently enabled omission of a step of decomposing and removing the catalyst after polymerization.
Since, however, the resulting olefin polymers or copolymers (to be sometimes referred to inclusively as olefin resins) still contain halogen components in an amount on the order of at least several hundred ppm, it has been desired to develop a technique which can effectively inhibit corrosion and coloration by an industrially simple and inexpensive means without adversely affecting the resulting olefin resins.
Previously, in an attempt to improve the surface properties of a molded article of an olefin resin such as dyeability, printability, coated film receptivity, or adhesion, there was suggested a composition comprising 100 parts by weight of a polyolefin and 0.5 to 300 parts by weight, preferably 20 to 60 parts by weight, of a complex metal hydroxide generically including hydrotalcites, or a product resulting from the removal of the water of crystallization therefrom (Japanese Pat. No. 37487/77). This Japanese patent discloses the improvement of the surface properties of polyolefin articles, but is quite silent on the corosion-causing tendency and coloration of olefin resins containing halogen components, and on the elimination of these troubles. The Japanese patent states that the effect of improving the surface properties intended is insufficient if the amount of the additive is not more than 3 parts by weight, especially not more than 0.5 part by weight, and recommends that for favorable results, the additive should be used in an amount of not less than 30 parts by weight per 100 parts by weight of the polyolefin. The Japanese patent neither discloses nor suggests that to avoid the corrosion-causing tendency and coloration, the BET specific surface area, average secondary particle size and crystallite size of hydrotalcites are critical.
It was suggested to incorporate a hydrotalcite having a BET specific surface area of not more than 30 m.sup.2 /g into a thermoplastic resin so as to improve its fire retardancy (Japanese Laid-Open Patent Publication No. 90192/77). The publication discloses that fire retardancy can be achieved by using the hydrotalcite in an amount of about 50 to about 150 parts by weight per 100 parts by weight of the thermoplastic resin. In this suggestion, too, the hydrotalcite is utilized in order to achieve an effect quite different from that intended by the present invention, and is quite silent on the corrosion-causing tendency and coloration of olefin resins containing halogen components. This Japanese Laid-Open Patent Publication neither describes nor suggests the importance of using hydrotalcites of specified BET specific surface area, average secondary particle size and crystallite size for the elimination of the aforesaid corrosion and coloration.
Some suggestions have also been made about the inhibition of corrosion or rust formation on metallic materials by halogen-containing olefin resins.
For example, Japanese Pat. No. 3541/58 discloses that in order to inhibit the corrosion of metallic material by an olefin resin such as polyethylene containing a halogen component obtained by polymerization with a Ziegler catalyst, a corrosion-inhibiting amount of a basic inorganic compound of a metal of Group II of the periodic table is incorporated in the olefin resin. This Japanese Patent Publication exemplifies calcium, magnesium, strontium, barium and zinc (in the order of decreasing effect) as the aforesaid metal, and the use of their oxides and hydroxides is recommended. Examples of these compounds given in the Patent Publication include calcium oxide, magnesium oxide, barium oxide, zinc oxide, calcium hydroxide, strontium oxide, strontium hydroxide, and barium hydroxide, the calcium oxide and calcium hydroxide being shown to be especially preferred. This Patent Publication is totally silent on hydrotalcites, however. Furthermore, as shown in Comparative Examples 2 and 3 hereinbelow, the use of magnesium oxide or magnesium hydroxide leads to insufficient corrosion resistance and also to a new trouble of yellowing molded articles prepared from the resulting resin composition. Moreover, the surface of the molded articles becomes rough.
Japanese Laid-Open Patent Publication No. 3947/74 discloses the incorporation into a halogen-containing olefin resin of a small amount of a compound selected from the group consisting of sodium oxide, potassium oxide, magnesium oxide, calcium oxide, zinc oxide, aluminum oxide, sodium hydroxide, potassium hydroxide, magnesium hydroxide, calcium hydroxide, zinc hydroxide, aluminum hydroxide, sodium aluminate, and sodium silicate. Satisfactory corrosion inhibition, however, cannot be obtained by this method, and moreover, new troubles such as coloration and surface roughening of molded articles produced from the resulting resin composition are caused.
Japanese Laid-Open Patent Publication No. 49258/77 suggests a polyolefin composition comprising a polyolefin produced by using a Ziegler catalyst and at least 0.01% by weight of a complex compound of the general formula EQU M.sub.x Al.sub.y (OH).sub.2x+3y-2z (A).sub.z.aH.sub.2 O
which may embrace hydrotalcites, which composition is provided in an attempt to remove the defects of the aforsaid conventional methods for inhibiting corrosion that may be caused by halogen-containing olefin resins. This Japanese patent document points out the trouble of yellowing of polyolefin compositions caused by the prior art techniques disclosed in Japanese Patent Publication No. 3541/58 or Japanese Laid-Open Patent Publication No. 3947/74 cited hereinabove, and suggests the use of the compound expressed by the above general formula in order to impart good corrosion resistance while avoiding these troubles. It also points out that a conventional technique of utilizing an alkaline earth metal fatty acid salt causes a new problem of deteriorating the properties of a polyolefin itself if this compound is used in an amount sufficient to exhibit an anticorrosive effect of practical value.
Japanese Laid-Open Patent Publication No. 49258/77, however, only discloses the use of hydrotalcites that may be embraced within the general formula, and does not at all state the properties of hydrotalcite particles which should be used. It does not even have the slightest recognition about the possible effects of the properties of the hydrotalcite particles on the anticorrosive effect, coloration inhibiting effect, the appearance of molded articles and the reproducibility of these effects.